Over the past several years, a number of different improvements have been mandated for the producers of high performance metals, such as metals used in critical aerospace, nuclear and other high-tech areas requiring high reliability requirements for the metals. For instance, in the melting of titanium or nickel-based materials where a high degree of cleanliness is required to enable the maximum in finished product integrity and dependability, the trend is toward the melting of materials in a trough-like retort which overflows into a secondary crucible for the production of an ingot or other metallurgical product. Such a product may consist of a shaped casting or may be further processed into a powder.
To date, the hearth or primary melting retort of conventional construction is primarily linear in shape and has a length in the range typically of 0.5 to 1.5 meters, depending upon the power and metallurgical requirements. By having a relatively long, shallow hearth or retort, metals can be melted in a longitudinal stream, allowing for sufficient time at a superheat temperature to allow removal of both high density and low density inclusions before being transferred to the secondary crucible or receptacle where the finished product is formed by secondary melting and shaping.
One of the problems associated with this type of hearth or retort relates to the feeding of loose raw materials and scrap into the retort. In hearth melting, a non-consumable heat source is normally used, such as an electron beam gun, plasma torch or a Rototrode. However, in all cases, it is necessary for the heat source to be in close proximity to the material feeder to enable melting the materials and advancing the materials along the length of the retort. This is achieved by maintaining a linear molten stream. This geometry limits not only the type of feed stock but also the design and manipulation of the feeder itself. The reasons for this is the proximity of the high energy melting arc or beam and the mechanical interference with the material feed means of the actual melting or heating source.
Because of these problems associated with conventional melting retorts, improvements are needed to avoid such problems. The present invention satisfies this need. Prior disclosures in this field include U.S. Pat. Nos. 2.982,534 and 3,150,961.